As a next-generation system of the W-CDMA (Wideband Code Division Multiple Access) and the HSDPA (High Speed Downlink Packet Access), an LTE system has been studied by 3GPP (3rd Generation Partnership Project) which is a standards body of the W-CDMA. In the LTE system as a radio access system, an OFDM (Orthogonal Frequency Division Multiplexing) scheme and an SC-FDMA (Single-Carrier Frequency Division Multiple Access) scheme have been studied to be applied to the downlink communications system and the uplink communications system, respectively (see, for example, Non Patent Document 1).
In the OFDM scheme, a frequency band is divided into plural sub-carriers having narrower frequency bands, and data are transmitted on each sub sub-carrier and the sub-carriers are closely arranged so as not to interfere with each other, so that fast data transmission can be achieved and an efficiency use of the frequency band can be improved.
In the SC-FDMA scheme, a frequency band is divided in a manner so that different frequencies can be separately used among plural terminals (user equipment terminals) and as a result, interferences between terminals can be reduced. Further, in the SC-FDMA scheme, a range of transmission power fluctuation can be made smaller; therefore lower energy consumption of terminals can be achieved and a wider coverage area can be obtained.
The LTE system is a communication system using shared channels in both downlink and uplink. For example, in downlink, a base station apparatus selects a mobile station (user equipment terminal) to communicate using the shared channel with respect to each sub-frame (each 1 ms) and transmits the shared channel to the selected mobile station. In this case, a process of selecting the mobile station to communicate as described above is called a scheduling process.
Further, in the LTE system, so-called Adaptive Modulation and Coding (AMC) is applied; therefore, transmission formats of the shared channels may vary among different sub-frames. Herein, the transmission format includes various information items indicating such as allocation information of the resource blocks which are frequency resources, modulation scheme, payload size, HARQ (Hybrid Automatic Repeat reQuest) information such as a Redundancy version parameter, a process number and the like, the number of streams, and a Pre-coding vector.
In the LTE system, identification information identifying the mobile station that communicates by using the shared channel in the sub-frame and the transmission format of the downlink shared channel are reported using Downlink Scheduling Information to be mapped to a Physical Downlink Control Channel (PDCCH). The Physical Downlink Control Channel (PDCCH) may also be called a DL L1/L2 Control Channel.    Non Patent Document 1: 3GPP TR 25.814 (V7.0.0), “Physical layer Aspects for Evolved UTRA,” June 2006